1. Field of the Invention
This invention relates to a brake control apparatus for an automobile, and more particularly to a brake control apparatus suitable for starting the automobile stopped facing upwardly on an inclined roadway.
2. Description of the Prior Art
Generally when the driver or operator will start the automobile stopped by a side braking system or a hand braking system, facing upwardly on an inclined roadway, the driver treads an accelerator pedal to raise the rotational speed of the internal combustion engine to a certain extent, while actuating a clutch pedal to softly press a clutch disc to a fly wheel in a clutch system. Such a condition of the clutch system is generally called "semi-clutching condition". Next, the driver further treads the accelerator pedal to gradually start the automobile, releasing the brake of the hand braking system and maintaining the semi-clutching condition.
As above described, when the automobile stopped on the inclined road-way will be started, the hand lever of the hand braking system, the clutch pedal and the accelerator pedal should be operated almost at the same time. Such operations are very difficult for the driver inexperienced in drive of the automobile. The inexperienced driver sometimes fails to start the automobile. At such a time, the automobile moves back to collide with another automobile in some cases.
Such a brake control operation to facilitate the start of the automobile stopped on the inclined roadway is known that includes a brake control valve which is closed by a movable valve member when the automobile is facing upwardly on the inclined roadway, to check brake fluid flow from a wheel cylinder to a master cylinder, and a cam shaft interconnected to a clutch pedal, having a cam portion positioned in a brake fluid passage. The brake control valve is arranged in a brake fluid conduit between the master cylinder and the wheel cylinder. The cam portion is displaced with actuation of the clutch pedal to displace the movable valve member to open and close the valve.
When the automobile using the above described brake control valve will be stopped facing upwardly on the inclined roadway, the master cylinder is actuated to apply the brake fluid pressure to the wheel cylinder. The clutch pedal is operated to disengage the clutch disc from the fly wheel in the condition that the brake fluid pressure is maintained in the brake fluid conduit. Thus, the valve is closed to check the brake fluid flow from the wheel cylinder to the master cylinder. Although the foot of the driver is removed from the brake pedal, the brake fluid pressure is held in the conduit between the valve and the wheel cylinder. For the start of the automobile, the clutch pedal is operated to softly press the clutch disc to the fly wheel, namely to put the clutch system into the semi-clutching condition. The valve is opened to release the brake fluid pressure held in the conduit. The accelerator pedal is treaded simultaneously with the clutch operation, to raise gradually the speed of the engine. The automobile is started without operation of the hand braking system. Thus, the automobile can be easily started even by the inexperienced driver.
However, the above brake control apparatus is arranged only in one of plural brake fluid pressure systems or conduits connecting the master cylinder and the wheel cylinders of the wheels. Accordingly, while the automobile is stopped on the inclined roadway, the wheel cylinders in the other brake fluid pressure systems are released from brake fluid pressure. In some cases, or on a steeply inclined roadway, the braking force in the one brake fluid pressure system is insufficient to keep the automobile stopping on the inclined roadway. The automobile moves back. An accident might occur.
In most of recent automobiles, one brake fluid pressure conduit is connected to front wheel cylinders, and another brake fluid pressure conduit is connected to rear wheel cylinders. Or one brake fluid pressure conduit is connected to a right front wheel cylinder and a left rear wheel cylinder, and another brake fluid pressure conduit is connected to a left front wheel cylinder and a right rear wheel cylinder. The former connections are called "front-rear connecting type", and the latter connections are called "X connecting type". A braking force applied by the one brake fluid pressure conduit is half as large as a braking force applied by both of the brake fluid pressure conduits.
In order to solve the above-described problem, this applicant proposed such a brake control apparatus that two brake control valves are arranged in the two brake fluid pressure conduits, respectively, and two balls as movable valve members are displaced by cam portions of a common cam shaft interconnected to a clutch pedal.
The problem of the insufficient braking force was solved by the above-described apparatus. However, a driving force of the cam shaft is considerably large for displacing the two balls. A fluid pressure is applied to the balls seated on the valve seats. A large treading force is required for actuating the clutch pedal. The clutch pedal is heavy. The clutch pedal is hard to be operated. In the start of the automobile, the release of the brake fluid pressure is apt to be late. The automobile does not smoothly start.